Efficient calculation of the ECO driving force for atomistic simulations of grain boundary motion
A. A. Schratt, V. Mohles.
A new formulation and implementation of the Energy Conserving Orientational (ECO) Driving Force (DF) for Molecular Dynamics (MD) simulations of grain boundary (GB) motion has been developed. While the original ECO-DF slows down MD simulations of GB motion by more than an order of magnitude, the new version is almost as efficient as the widely used Janssens DF (J-DF). In order to rate the new method in comparison to others, the velocity of a symmetric Σ5 〈001〉 36.87° tilt GB in nickel has been simulated using the new ECO-DF and the J-DF. The deviations are discussed, including the impacts on the AIRwalk method to evaluate the GB mobility. The temperature T, the DF magnitude p, and the boundary conditions were varied. Under fully periodic boundaries, all results consistently yield a GB velocity v(p, T) that is based on two subsequent or co-dependent mechanisms, shuffling and its initiation, just like for a symmetric Σ7 〈111〉 38.2° tilt GB investigated previously with the original ECO-DF. Under the so-called shrink-wrapped boundary conditions, a relative grain displace- ment occurs. The magnitude of this coupling effect strongly depends on temperature. From the comparison of simulations under different boundary conditions it appears probable that the initiation process under periodic boundary conditions is actually the initiation of GB sliding, which needs to undo fully coupled grain motion. The shuffling mechanism is the combined GB motion fully coupled with grain displacement.
Atomistic simulations of grain boundary motion utilising a new, efficient implementation of the energy-conserving orientational driving force were performed with different boundary conditions and compared to existing methods and simulation results. Simulations with open and periodic boundary conditions differ drastically in the mechanisms of grain boundary motion.